The invention relates to a method and machine for connecting a sheet-like wrapping material (e.g., a continuous web of cigarette paper or portions of such web) with rod-shaped smokers' products including fillers of tobacco or filter material, filter mouthpieces, plain cigarettes, groups of coaxial or parallel cigarettes or the like. More particularly, the invention relates to a method and machine for connecting a sheet-like wrapping material with rod-shaped smokers' products by means of a hotmelt, i.e., an adhesive which (in contrast to the so-called wet adhesives) is activated in response to heating and sets in response to cooling.
It is already known to apply an aqueous dispersion of polyvinyl acetate glue to a web of cigarette paper or similar sheet-like material which is used as a wrapper for tobacco fillers and/or fillers consisting of fibrous or other filter material and/or as a means for uniting filter rod sections with plain cigarettes, cigars or cigarillos. If the dispersion is applied to a continuous web of cigarette paper, it normally forms a layer along one marginal portion of the web. The web is thereupon draped around a rod-like filler of tobacco or filter material so that the adhesive-coated marginal portion overlies the other marginal portion of the resulting tubular wrapper, i.e., the overlapping marginal portions form a seam which extends in parallelism with the axis of the wrapped filler and is heated to expel water from the adhesive layer and thereby to insure the establishment of a reliable bond in response to activation and subsequent setting of hotmelt.
In a modern mass-producing cigarette maker or filter rod maker, the web of wrapping material is transported at a very high speed (normally in the range of 400-500 meters per minute). Therefore, the interval of time which is available for expulsion of water from an aqueous dispersion of hotmelt is extremely short. In other words, if the temperature at which the dispersion is heated to expel water from the applied adhesive coat is relatively low, the interval of time for expulsion of water is too long except if the dimensions of the machine are increased for the express purpose of allotting the necessary time for drying of the seam. Alternatively, it is necessary to increase greatly the temperature in the region where the coat of diluted hotmelt is subjected to a drying action. This is undesirable for a number of reasons, especially when the machine is brought to a standstill, because the wrapping material is likely to be charred or to go up in flames unless the machine is equipped with complex, costly and highly sensitive heat sensing devices.
The situation is analogous in certain packing machines for arrays of plain or filter tipped rod-shaped smokers' products wherein such arrays are confined in packets consisting of one or more suitably deformed blanks made of paper, cardboard, metallic foil or synthetic plastic material. Portions of certain blanks must be bonded to each other by one or more layers of adhesive.